Re: pcre extended character class support

On 25 July 2025 23:17:43 BST, Niels Dossche <dossche.niels@gmail.com> wrote: >Hi internals > >On PHP 8.5-dev, we ship with pcre2lib 10.45. > >This includes a new opt-in feature called "PCRE2_ALT_EXTENDED_CLASS". >It enables the use of complex character set operations in accordance to UTS#18 (Unicode >Technical Standard 18). >This means it becomes possible to nest character sets, perform set operations on them, etc. >One example of such a set operation is a set subtraction, e.g. the regex >"[\ep{L}--[QW]]" means "Unicode letters other than Q and W". >Or a more realistic example (inspired from [1]): the regex "[\p{Lu}--[0-9]]" matches >all non-ASCII unicode numbers. >You can also do ORs, ANDs, etc. > >The reason this is opt-in in pcre2lib, is because the interpretation of existing regexes may >change. >This standard is being adopted in other languages too, also opt-in, for example in JavaScript >[1]. >To expose this functionality in PHP, we also have to make it opt-in via a modifier. > >In JavaScript, this is enabled via the /v modifier at the end of the regex [1]. >This does the same thing as the /u modifier, but extends it with this UTS#18 standard. >We also already have /u in PHP that enables UTF-8 unicode mode. So we could do the same as >JavaScript and add a /v modifier that extends /u and also enables PCRE2_ALT_EXTENDED_CLASS. >Technically, you don't need unicode processing for enabling PCRE2_ALT_EXTENDED_CLASS, but as it >comes from a unicode standard (and that at least JavaScript does this too), it may make sense to >enable them both. > >The actual patch is trivial: >```diff >diff --git a/ext/pcre/php_pcre.c b/ext/pcre/php_pcre.c >index 8e0fb2cce5f..4a4727545ad 100644 >--- a/ext/pcre/php_pcre.c >+++ b/ext/pcre/php_pcre.c >@@ -718,6 +718,9 @@ PHPAPI pcre_cache_entry* pcre_get_compiled_regex_cache_ex(zend_string >*regex, bo > case 'S': /* Pass. */ break; > case 'X': /* Pass. */ break; > case 'U': coptions |= PCRE2_UNGREEDY; break; >+#ifdef PCRE2_ALT_EXTENDED_CLASS >+ case 'v': coptions |= PCRE2_ALT_EXTENDED_CLASS; ZEND_FALLTHROUGH; >+#endif > case 'u': coptions |= PCRE2_UTF; > /* In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII > characters, even in UTF-8 mode. However, this can be changed by setting > >``` > >What do we think? > >[1] https://github.com/tc39/proposal-regexp-v-flag Yes, please. cheers Derick